206 BOTANICAL GAZETTE ■ * [mmch 



The spindle becomes narrower and more pointed and the connect- 

 ing fibers, apparently contracting while the spindle is lengthening, 

 gradually draw the chromosomes into a perfect circle in the equatorial 

 plane (figs. 44-60). In fig. 48 the spindle is distorted. This was 

 probably produced by the unequal contraction of the cytoplasm. 

 Figs. 39, 43, 47, 57, 60, 61 make a series, showing how the chromo- 

 somes are drawn from their scattered positions into the symmetrical 

 figure of the mother star. A large number of figures of this stage 

 have been included in order to show all the ordinary types of develop- 

 ing spindles to be seen in Agave. In some, the connecting fibers are 

 prominent; in others, especially as the chromosomes approach the 

 equator, one sees only a dark-staining central mass. It is important 

 to note that the spindle fibers appear thickest and densest in their 

 central parts, even in very young spindles. Apparently the chromo- 

 somes are attached to the spindle fibers from the beginning. The 

 crowding of the chromosomes against the nuclear wall, as shown in 

 in figs. 23, 30, brings the chromosomes into a position where their 

 fusion with the spindle fibers can be accomplished. 



The mechanism for bringing the chromosomes from their scattered 

 position into the symmetrical wreath of the mother star is compara- 

 tively simple, requiring only the shortening of the connecting fibers, 

 combined with a pull from the spindle threads exerted from the 

 poles. The action of the spindle as well as the attachments must be 

 looked upon as being accomplished by a viscid substance, perhaps 

 under the influence of attractive and repulsive forces. If the sub- 

 stance is contractile in the ordinary sense of the word, it mu 

 acquire this property after development. 



Multipolar figures.— Multipolar figures were not numerous. I \ 

 may have been because of the comparatively small size of the mice 

 and the thickness of the sections. A special study was made of t e 

 multipolar figures found, and the conclusion was reached that W 

 were . all artifacts. The various types are shown in the series pi • 

 6 4-7 3- Fig. 64 is a diagonal section, included to show the charactf 

 and position of the chromosomes in the mother star. Both poles a^ 

 cut away, one end more than the other. Figs. 65, 66 are tan & e ^' he 

 sections representing small parts of the nucleus and spindle, 

 fibers are both spindle and connecting fibers and make an appe 



